The UTV-owned station fired Whale for his comments, which he made during a live phone-in show on March 20 this year in the runup to the London mayoral elections.

TalkSport was fined £20,000 for a breach of the broadcasting code and ordered by Ofcom to broadcast a statement of its findings.

The regulator said the broadcaster had "seriously breached the due impartiality rules at the time of an election".

"The presenter directly encouraged listeners to vote for Boris Johnson in the upcoming London mayoral elections and criticised Ken Livingstone," Ofcom added.

"Breaches of this nature have the potential to cause considerable harm to the democratic process by conferring an unfair electoral advantage on a particular candidate."

Whale was fired by TalkSport in May following an internal investigation. The presenter launched legal action against the station but later dropped it, saying he did not have the funds to continue.

Ofcom rejected a claim by TalkSport management that Whale's breach of the regulations was a "one-time rant", saying the presenter reiterated his support for Johnson at several times during the programme.

Whale told listeners that Livingstone had "been nothing but a complete and utter tragedy for the capital city" and said that under Johnson they would not be "ripped off nearly as much, if at all".

He added that if people did not vote for Johnson they had only themselves to blame if "Livingstone gets in for another term". Three people complained about Whale's comments.

Ofcom said the broadcast was on matters of "major political controversy" and "had the potential to cause considerable harm to the democratic process".

"The presenter's comments were not simply a 'vote for…' comment but amounted to a direct political message to his listeners. This effectively resulted in the programme becoming a platform in support of Boris Johnson and critical of Ken Livingstone," added the regulator.

Ofcom said TalkSport had already been warned following a breach of impartiality rules by the station's former presenter George Galloway, who used his show to announce he would be standing against a government minister at the next general election.

The regulator said the station had failed to take sufficient action following the breach in August last year.

"It was the second time within eight months that the station breached the code's due impartiality requirements … TalkSport could and should have taken more action to ensure more robust compliance both before and on the date of [Whale's] broadcast," Ofcom added.

TalkSport management told Ofcom that it had delayed informing Whale he had been sacked until after the London election "so as not to compromise the election in any way".

In its evidence to the regulator, TalkSport said Whale's producer had decided not to take him off air when he made the comments because "this could have inflamed the issue".

Station management said the option of taking the station off air would have been "nuclear" and had been ruled out.

Whale has now returned to full-time radio presenting on Global Radio's London station, LBC 97.3.

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